Dansette major rectifier - UK Vintage Radio Repair and Restoration Discussion Forum

leslie5555 · 19th Sep 2018, 9:25 pm

Uses amp type MC/1961/ but the one with the UL84 valve.
I checked the contact cooled rectifier and it was only reading 125vdc I tacked in a IN4007 and rechecked it and it went up slightly but only to 150vdc
The mains measures 245vac
I have changed the waxy .05 UF cap and a 10K resistor .
What else should I be checking ?

Herald1360 · 19th Sep 2018, 9:29 pm

How exactly, relative to the existing rectifier, did you tack in the 1N4007?

Instead of, with a 100R or so series resistor is best. A parallel 10n 400V capacitor doesn't come amiss either to shut up reverse recovery hash.

Have you checked the cathode resistor and its parallel electrolytic for any problems? The UL84 may be pulling excess current.

leslie5555 · 20th Sep 2018, 7:02 am

I disconnected the leads from the rectifier to temporarily tack in the diode ,
I swapped the UL84 for another in good working condition
The 120ohm resistor was checked and is ok the other which is 10k has been changed and I used a 2w type
I will look into the other checks you have suggested thank you Chris

Peter.N. · 20th Sep 2018, 9:58 am

What is the AC voltage going into the diode? If it's anything like 240v I would think the reservoir capacitor is open circuit.

Peter

leslie5555 · 20th Sep 2018, 11:35 am

Not 100% sure how to check this am I right in thinking that I connect one lead to the cathode of the diode and the other to the negative on the can?

ms660 · 20th Sep 2018, 11:40 am

Meter set to read at least 250 volts AC, one meter probe to the anode of the rectifier the other meter probe to chassis/HT-ve.

Lawrence.

leslie5555 · 20th Sep 2018, 12:04 pm

Ok thanks , did that and got 140v ac?

ms660 · 20th Sep 2018, 12:09 pm

What's the AC voltage coming out of the transformer?

Lawrence.

leslie5555 · 20th Sep 2018, 12:16 pm

130v

ms660 · 20th Sep 2018, 12:22 pm

Something wrong there, more going into the rectifier than what's coming out of the transformer, I must confess I've not come across a one valve U series version that uses a selenium rectifier, maybe someone else has.

Lawrence.

leslie5555 · 20th Sep 2018, 12:33 pm

There are other threads on here that refer to the same amp with the ul84 there is a similar amp with el84 .
Back to the voltage it may be I'm not checking it correctly as you may have gathered I'm not to sure where to connect the dmm leads so in this case I connected one lead to the black wire from the tx to chassis the other to the blue lead which is connected to the Mr ?

Herald1360 · 20th Sep 2018, 12:39 pm

Single valve UL84 and solid state rectifier sounds very odd. Are you sure it's a UL84?

Only Major cct I can find shows EL84.

Edit: Bit slow......

Edit 2: A bit more digging suggests that a transformer fed UL84 Major does exist. And that a UL84 can happily run with 100-170V on its anode. Power output suffers at the lower end. Maybe there's nothing actually wrong......?

leslie5555 · 20th Sep 2018, 12:55 pm

It is a Ul84 valve and the chassis has UL84 printed on it I will post a pic later I've trawled through various threads about this and the ul84 always seems to cause a lot of confusion and debate as to whether its the correct valve for this amp

leslie5555 · 20th Sep 2018, 1:07 pm

Here are some photos

leslie5555 · 20th Sep 2018, 1:12 pm

Quote:

Originally Posted by Herald1360

Edit 2: A bit more digging suggests that a transformer fed UL84 Major does exist. And that a UL84 can happily run with 100-170V on its anode. Power output suffers at the lower end. Maybe there's nothing actually wrong......?

Well I will be pleased to learn that there's nothing wrong with this it does work fine albeit a little lacking is bass but I think that's to be expected

Edward Huggins · 20th Sep 2018, 2:45 pm

Quote:

Originally Posted by ms660

Something wrong there, more going into the rectifier than what's coming out of the transformer, I must confess I've not come across a one valve U series version that uses a selenium rectifier, maybe someone else has.

These were "transitional" single-stage amplifiers made by Dansette. The first (1954/55) versions used an UL41, and then given their stock of 45V tapped mains transformers, they used an UL84 from about 1956. These then migrated to the EL84 version which continued to be made for many years well into the mid 1960s. They all used contact cooled rectifiers. Edward

crackle · 20th Sep 2018, 3:19 pm

Did you check the cathode resistor and electrolytic.

Mike

leslie5555 · 20th Sep 2018, 4:36 pm

Hi Mike I did check the cathode resistor and yet to check the electrolytic thanks

Station X · 20th Sep 2018, 4:41 pm

What form did the check take and what was the result?

leslie5555 · 20th Sep 2018, 6:11 pm

I checked the resistance and it was 114ohms its value is 120ohms

19th Sep 2018, 9:25 pm	#1
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Dansette major rectifier Uses amp type MC/1961/ but the one with the UL84 valve. I checked the contact cooled rectifier and it was only reading 125vdc I tacked in a IN4007 and rechecked it and it went up slightly but only to 150vdc The mains measures 245vac I have changed the waxy .05 UF cap and a 10K resistor . What else should I be checking ?

19th Sep 2018, 9:29 pm	#2
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Dansette major rectifier How exactly, relative to the existing rectifier, did you tack in the 1N4007? Instead of, with a 100R or so series resistor is best. A parallel 10n 400V capacitor doesn't come amiss either to shut up reverse recovery hash. Have you checked the cathode resistor and its parallel electrolytic for any problems? The UL84 may be pulling excess current. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

20th Sep 2018, 7:02 am	#3
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier I disconnected the leads from the rectifier to temporarily tack in the diode , I swapped the UL84 for another in good working condition The 120ohm resistor was checked and is ok the other which is 10k has been changed and I used a 2w type I will look into the other checks you have suggested thank you Chris Last edited by leslie5555; 20th Sep 2018 at 7:19 am.

20th Sep 2018, 9:58 am	#4
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Dansette major rectifier What is the AC voltage going into the diode? If it's anything like 240v I would think the reservoir capacitor is open circuit. Peter

20th Sep 2018, 11:35 am	#5
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier Not 100% sure how to check this am I right in thinking that I connect one lead to the cathode of the diode and the other to the negative on the can?

20th Sep 2018, 11:40 am	#6
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Dansette major rectifier Meter set to read at least 250 volts AC, one meter probe to the anode of the rectifier the other meter probe to chassis/HT-ve. Lawrence. Last edited by ms660; 20th Sep 2018 at 11:51 am. Reason: addition

20th Sep 2018, 12:04 pm	#7
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier Ok thanks , did that and got 140v ac?

20th Sep 2018, 12:09 pm	#8
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Dansette major rectifier What's the AC voltage coming out of the transformer? Lawrence.

20th Sep 2018, 12:16 pm	#9
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier 130v

20th Sep 2018, 12:22 pm	#10
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Dansette major rectifier Something wrong there, more going into the rectifier than what's coming out of the transformer, I must confess I've not come across a one valve U series version that uses a selenium rectifier, maybe someone else has. Lawrence.

20th Sep 2018, 12:33 pm	#11
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier There are other threads on here that refer to the same amp with the ul84 there is a similar amp with el84 . Back to the voltage it may be I'm not checking it correctly as you may have gathered I'm not to sure where to connect the dmm leads so in this case I connected one lead to the black wire from the tx to chassis the other to the blue lead which is connected to the Mr ?

20th Sep 2018, 12:39 pm	#12
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: Dansette major rectifier Single valve UL84 and solid state rectifier sounds very odd. Are you sure it's a UL84? Only Major cct I can find shows EL84. Edit: Bit slow...... Edit 2: A bit more digging suggests that a transformer fed UL84 Major does exist. And that a UL84 can happily run with 100-170V on its anode. Power output suffers at the lower end. Maybe there's nothing actually wrong......? __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O Last edited by Herald1360; 20th Sep 2018 at 12:55 pm.

20th Sep 2018, 12:55 pm	#13
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier It is a Ul84 valve and the chassis has UL84 printed on it I will post a pic later I've trawled through various threads about this and the ul84 always seems to cause a lot of confusion and debate as to whether its the correct valve for this amp

20th Sep 2018, 1:07 pm	#14
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier Here are some photos Attached Thumbnails

20th Sep 2018, 3:19 pm	#17
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Dansette major rectifier Did you check the cathode resistor and electrolytic. Mike

20th Sep 2018, 4:36 pm	#18
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier Hi Mike I did check the cathode resistor and yet to check the electrolytic thanks

20th Sep 2018, 4:41 pm	#19
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,287	Re: Dansette major rectifier What form did the check take and what was the result? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

20th Sep 2018, 6:11 pm	#20
leslie5555 Heptode Join Date: May 2015 Location: Reading, Berkshire, UK. Posts: 692	Re: Dansette major rectifier I checked the resistance and it was 114ohms its value is 120ohms